Bump amplitude, but not latency and time-course, can depend on position of illumination in Limulus photoreceptor cells

1993 ◽  
Vol 173 (3) ◽  
pp. 377-383 ◽  
Author(s):  
H. Reu� ◽  
H. Stieve
Keyword(s):  
Time Course ◽  
Photoreceptor Cells ◽  
Limulus Photoreceptor

scholarly journals Regulation of intracellular cyclic GMP concentration by light and calcium in electropermeabilized rod photoreceptors.

1994 ◽  
Vol 103 (1) ◽  
pp. 67-86 ◽  
Author(s):  
V J Coccia ◽  
R H Cote
Keyword(s):  
Steady State ◽  
Guanylate Cyclase ◽  
Time Course ◽  
Calcium Concentration ◽  
Fold Increase ◽  
Photoreceptor Cells ◽  
Cyclase Activity ◽  
Free Calcium ◽  
Guanylate Cyclase Activity ◽  
Steady State Levels

This study examines the regulation of cGMP by illumination and by calcium during signal transduction in vertebrate retinal photoreceptor cells. We employed an electropermeabilized rod outer segment (EP-ROS) preparation which permits perfusion of low molecular weight compounds into the cytosol while retaining many of the features of physiologically competent, intact rod outer segments (ROS). When nucleotide-depleted EP-ROS were incubated with MgGTP, time- and dose-dependent increases in intracellular cGMP levels were observed. The steady state cGMP concentration in EP-ROS (0.007 mol cGMP per mol rhodopsin) approached the cGMP concentration in intact ROS. Flash illumination of EP-ROS in a 250-nM free calcium medium resulted in a transient decrease in cGMP levels; this occurred in the absence of changes in calcium concentration. The kinetics of the cGMP response to flash illumination of EP-ROS were similar to that of intact ROS. To further examine the effects of calcium on cGMP metabolism, dark-adapted EP-ROS were incubated with MgGTP containing various concentrations of calcium. We observed a twofold increase in cGMP steady state levels as the free calcium was lowered from 1 microM to 20 nM; this increase was comparable to the behavior of intact ROS. Measurements of guanylate cyclase activity in EP-ROS showed a 3.5-fold increase in activity over this range of calcium concentrations, indicating a retention of calcium regulation of guanylate cyclase in EP-ROS preparations. Flash illumination of EP-ROS in either a 50- or 250-nM free calcium medium revealed a slowing of the recovery time course at the lower calcium concentration. This observation conflicts with any hypothesis whereby a reduction in free calcium concentration hastens the recovery of cytoplasmic cGMP levels, either by stimulating guanylate cyclase activity or by inhibiting phosphodiesterase activity. We conclude that changes in the intracellular calcium concentration during visual transduction may have more complex effects on the recovery of the photoresponse than can be accounted for solely by guanylate cyclase activation.

Photoreceptor cells with unusual functional properties on the ventral nerve of Limulus

1999 ◽  
Vol 16 (6) ◽  
pp. 1191-1197 ◽  
Author(s):  
KÁROLY NAGY ◽  
MARLIES DORLÖCHTER ◽  
SVENJA KLÄSEN ◽  
DANNY STEINBUSCH
Keyword(s):  
Time Course ◽  
Single Photon ◽  
Receptor Potential ◽  
Photoreceptor Cells ◽  
Light Sensitivity ◽  
Atpase Inhibitor ◽  
Decay Kinetics ◽  
Normal Cells ◽  
Inward Current ◽  
Low Efficiency

Normal photoreceptor cells on the ventral nerve of Limulus respond to a moderately intense flash with a large receptor potential or current. Occasionally, cells are found in which the same flash evokes only a small receptor potential or current. Our investigations reveal physiological reasons for the poor light sensitivity in these “unusual cells.” In unusual cells prolonged illumination with intense light evokes a step-like inward current with an amplitude of some nanoamperes, but without a large transient peak. The current appears to be summed up of single photon responses with amplitudes smaller than about 50 pA. Their time course is similar to that of small single photon responses forming the so-called macroscopic C1 component in normal cells. The macroscopic current evoked by an intense flash has slow activation and deactivation kinetics and reaches a saturated amplitude of about 4–5 nanoamperes. The light-intensity dependence of the current evoked by flashes or by prolonged illumination has a slope of about 1 in log–log plots. The decay kinetics of the current is similar to that of the C1 component measured in normal cells after the block of the C2 component. Occasionally, the step-like current is superposed by large standard bumps. These bumps are blocked by the Ca2+-ATPase inhibitor cyclopiazonic acid, while the sustained inward current persists. We conclude that in unusual cells the light-activated current is identical to the C1 component of normal cells. The phospholipase C pathway that in normal cells presumably gives rise to the C2 component functions only with a low efficiency in unusual cells.

Ionic mechanisms of phototransduction in photoreceptor cells from the epistellar body of the octopus eledone cirrhosa

1999 ◽  
Vol 202 (8) ◽  
pp. 977-986
Author(s):  
C.S. Cobb ◽  
R. Williamson
Keyword(s):  
Time Course ◽  
Sea Water ◽  
Light Flash ◽  
Receptor Potential ◽  
Photoreceptor Cells ◽  
Evoked Response ◽  
Na Channel ◽  
External Application ◽  
Ionic Mechanisms ◽  
Potential Activity

Intracellular recordings were made from extraocular photoreceptor cells within isolated epistellar bodies of the lesser or northern octopus Eledone cirrhosa. The cells had resting potentials around −41+/−5 mV (mean +/− s.d., N=60) and showed light-flash-induced membrane depolarisation. The evoked response to a brief light flash consisted of a transient peak depolarisation, followed by a plateau component. The magnitude of the light-induced peak depolarisation response was decreased by bathing the epistellar body in artificial sea water (ASW) low in Na+, where choline+ replaced Na+, or by passing steady depolarising current. Replacement of external Na+ by Li+ had no effect on the light-stimulated response. The external application of the Na+ channel blocker tetrodotoxin (3 micromol l-1) increased the light-evoked response, but this was accompanied by a loss of action potential activity. The amplitude and duration of the response to a light flash was increased by bathing the epistellar body in ASW low in Ca2+, or in ASW containing 10 mmol l-1 Co2+, and after intracellular microinjection of the Ca2+ buffer EGTA. Intracellular microinjection of Ca2+ or inositol 1,4,5-trisphosphate, or external application of the phospholipase C inhibitor U-73122, had no apparent effect on the light-evoked response. These results are consistent with the interpretation that (1) the majority of the light-induced inward current is carried by Na+, probably via a non-selective cation channel, and (2) an increase in the intracellular free Ca2+ concentration, mediated by the phototransduction process, is involved in regulating the light-induced inward photocurrent and thus, in effect, determines the amplitude, time course and sensitivity of the receptor potential.

An electrically evoked slow potential of the frog's retina. I. Properties of response

1975 ◽  
Vol 38 (1) ◽  
pp. 185-197 ◽  
Author(s):  
R. W. Knighton
Keyword(s):  
Time Constant ◽  
Time Course ◽  
Outward Current ◽  
Electrical Current ◽  
Photoreceptor Cells ◽  
Base Line ◽  
Slow Potential ◽  
Chemical Agents ◽  
Electrical Stimuli ◽  
Retinal Response

1. Brief pulses of electrical current passed through the frog's eye cup from sclera to vitreous (inward current) evoked large, vitreous positive slow potentials of retinal origin. Brief pulses of outward current evoke no response. 2. This electrically evoked retinal response (EERG) increased sharply in amplitude as the strength of the stimulus was increased. 3. Strength-duration curves showed that the stimulating pulse was integrated with a time constant ranging from 14 to 36 ms. The time constant was a function of the amplitude chosen as a criterion. 4. The EERG was abolished by chemical agents which abolish the PII component of the ERG (KCl, NH3, aspartate). 5. The waveform of the EERG returned to the base line with exactly the same time course as the PII component of the ERG, both when the PII was evoked by flashes of light and when it was evoked by flashes of darkness. 6. These results can be explained in terms of the hypothesis that electrical stimuli act on the synaptic terminals of the photoreceptor cells.

Opsin expression in the rat retina is developmentally regulated by transcriptional activation

1988 ◽  
Vol 8 (4) ◽  
pp. 1570-1579
Author(s):  
J E Treisman ◽  
M A Morabito ◽  
C J Barnstable
Keyword(s):  
Transcriptional Activation ◽  
Time Course ◽  
Photoreceptor Cells ◽  
Opsin Gene ◽  
Rod Photoreceptor ◽  
Developmentally Regulated ◽  
Photoreceptor Layer ◽  
Opsin Expression ◽  
Rna Accumulation ◽  
Nascent Transcripts

The gene for rhodopsin, the primary light sensor of the visual system, is specifically expressed in the rod photoreceptor cells of the retina. We show here that in the rat, opsin RNA first accumulates to detectable levels at postnatal day 2 (PN2) and that nascent transcripts can be detected at PN1; this is the time when peak numbers of photoreceptor cells are generated by the final division of their neuroepithelial precursors. Accumulated opsin RNA then increases to reach the adult level, 0.06% of total retinal RNA, at about PN10. The transcription rate of the opsin gene increases to a similar extent over the same time course between PN3 and adulthood, suggesting that transcriptional activation is responsible for the increase in opsin expression. We used the antibody RET-P1 to show that rhodopsin protein is also detectable at PN2 and that the number of cells expressing the protein increases with time in a central-to-peripheral gradient in the retina. This increase in the number of differentiating photoreceptors in the tissue appears to account for much of the increase in opsin gene transcription and RNA accumulation. In situ hybridization to opsin RNA shows that it is restricted to the photoreceptor layer from the time it can first be detected, at PN7. Later in development, when RET-P1 staining shifts to the photoreceptor outer segments, opsin RNA becomes localized to the inner segments, suggesting that the distributions of opsin protein and RNA are related.

scholarly journals Light Adaptation of Discrete Waves in the Limulus Photoreceptor

1972 ◽  
Vol 60 (1) ◽  
pp. 86-101 ◽  
Author(s):  
Richard Srebro ◽  
Mahmood Behbehani
Keyword(s):  
Time Course ◽  
Light Adaptation ◽  
Limulus Photoreceptor ◽  
Average Size ◽  
Effect Of Light

Light adaptation affects discrete waves in two ways. It reduces their average size and decreases the probability that a photon incident at the cornea causes a discrete wave. There is no effect of light adaptation on the latency of discrete waves, or on their time-course.

scholarly journals Opsin expression in the rat retina is developmentally regulated by transcriptional activation.

1988 ◽  
Vol 8 (4) ◽  
pp. 1570-1579 ◽  
Author(s):  
J E Treisman ◽  
M A Morabito ◽  
C J Barnstable
Keyword(s):  
Transcriptional Activation ◽  
Time Course ◽  
Photoreceptor Cells ◽  
Opsin Gene ◽  
Rod Photoreceptor ◽  
Developmentally Regulated ◽  
Photoreceptor Layer ◽  
Opsin Expression ◽  
Rna Accumulation ◽  
Nascent Transcripts

The gene for rhodopsin, the primary light sensor of the visual system, is specifically expressed in the rod photoreceptor cells of the retina. We show here that in the rat, opsin RNA first accumulates to detectable levels at postnatal day 2 (PN2) and that nascent transcripts can be detected at PN1; this is the time when peak numbers of photoreceptor cells are generated by the final division of their neuroepithelial precursors. Accumulated opsin RNA then increases to reach the adult level, 0.06% of total retinal RNA, at about PN10. The transcription rate of the opsin gene increases to a similar extent over the same time course between PN3 and adulthood, suggesting that transcriptional activation is responsible for the increase in opsin expression. We used the antibody RET-P1 to show that rhodopsin protein is also detectable at PN2 and that the number of cells expressing the protein increases with time in a central-to-peripheral gradient in the retina. This increase in the number of differentiating photoreceptors in the tissue appears to account for much of the increase in opsin gene transcription and RNA accumulation. In situ hybridization to opsin RNA shows that it is restricted to the photoreceptor layer from the time it can first be detected, at PN7. Later in development, when RET-P1 staining shifts to the photoreceptor outer segments, opsin RNA becomes localized to the inner segments, suggesting that the distributions of opsin protein and RNA are related.

The pH Dependence of the Receptor Potential of the Hermit Crab Photoreceptor

1974 ◽  
Vol 29 (3-4) ◽  
pp. 147-156 ◽  
Author(s):  
H. Stieve ◽  
T. Malinowska
Keyword(s):  
Hermit Crab ◽  
Time Course ◽  
Compound Eye ◽  
Ph Dependence ◽  
Receptor Potential ◽  
Photoreceptor Cells ◽  
Alkaline Solutions ◽  
Ph Effects ◽  
Good Reproducibility ◽  
Acidic Environments

Abstract The pH dependence of the receptor potential (ReP) of isolated layers of photoreceptor cells from the hermit crab compound eye (Eupagurus bernhardus L.) was determined. Measurements were performed, using extracellular electrodes, in the range pH 3.5 - 9.5 in three different buffer systems: Tris, glycine, and phosphate. The amplitude of the ReP was highest at pH 7.5 and decreased in more acidic and more alka­line salines (Fig. 4). Relative to the changes in ReP amplitude, the changes in time course and shape of ReP were small. Salines of pH other than 7.5 caused an increase of the latent period but decreased the peak amplitude time and the repolarizing phase (t2). Alkaline salines caused about the same changes in the ReP as acidic salines. The only observed difference was that repolarisation was more strongly influenced by alkaline solutions and that the plateau magnitude was depressed relatively more than the peak magnitude in acidic environments. Of the three buffers used, Tris had the weakest influence on the ReP and phosphate buffer the strongest. In contrast to the good reproducibility of the experimental results, the reversibility of the pH effects was generally poor; the effects with glycine-buffer were more reversible than those with Tris.

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